Drilling brass

So I was making some brass bearings at the weekend, drilling and reaming for the crankshaft....

My debate was - do I drill/ream dry or with some cutting fluid?

Using cutting fluid I found that the drill will clog easily and then it will scream away. So my thoughts was dry was better.

Comments? (I know...I am still learning)

Brass always dry

Dry for brass, FWIW... also take the edge off the drills with a stone or diamond lap... stops drills snatching as they break through, I also find WD40 helps for aluminium.

George

Me too - although I do mine on the bench grinder. I bought a drill-set specially for brass and modify them as I go along.

Apart from fixing the break-though issue it also stops the grabbing/pull-ahead when opening up a previous hole or drilling in stages.

....but of course it really means you need a set of drills for brass independent to drills for other materials. Unless someone likes sharpening drills every 5 minutes!

Stoning the cutting edges of drills for brass has never worked properly for me; they still have a tendency to snatch. So for brass and bronze I am building up a collection of slow helix drills, designed for brass, as I need them.

Andrew

I have a few half round drills that I use exclusively on brass.

On the contrary, i was told brass needed a very sharp cutting point, i'm not sure however, if what you mean by stoning is either to refine the edge or to round it. I have a very dirty old book on fitting where the author goes at some length to expound the virtues of using the "correct" point angles on drills for certain materials. A greater lead angle will graduate the load on the tool before it reaches full cutting diameter. The "grab" of a drill can happen because the chisel point is not able to "shear" to full size in one go, so it digs in and is essentially stuck in the work piece.

This advice obviously needs context and a sense of proportion,though as the occasional need for drilling brass shouldn't need this much fuss, a standard drill point would be fine. If you're going through those horrid chips like no tomorrow, in a jobbing workshop, then you might want to think about it.

To answer the question though, i myself would cut brass dry, but when it comes to tapping and reaming, high load operations in their own right, it's only sensible to consider a cutting fluid to reduce heat and aid flow of channels of swarf, this much yields a benefit almost regardless of the material being cut.

The tool is only screaming (singing as i used to call it) because either you're "dithering the feed" or more likely the machine is going too fast for the operation. What you don't want is to temper the tool by getting it too hot as this will ruin the finish. Without seeing what happens it's often hard to pinpoint the exact cause but i also suspect that vibration at the head of the tool can do this if too much of the shank is protruding from it's holder.

It also helps to understand a bit more about the nature of the alloy being cut as brass, bronze, copper, gunmetal all come in so many differing varieties, the cutting qualities between them vary also.

The drill is always worse towards the end of it's cut when it has the last web to cut out and breach through.

For an extremely fine finish on metals, modern HSS doesn't have a fine enough grain structure, this is a herring though and i dont, nor am i ever going to be able to compete with the quaity of tool rooms who can afford muffle furnaces and what not.

So basically my votes on keep it sharp and dry for a cut, but well lubed up for a reamer. When cutting keyways for example, i often put more oil than a fish n chip shop and i havent broken one yet. I'd be tempted to treat the reamer with the same slimey respect. The only other point i've left out is it depends how much work you're leaving for the reamer to do.

Michael W

Edited By Michael Walters on 03/05/2016 03:31:24

Michael W, you are right in saying the tools for brass must be sharp, what is meant by stoning of the edge is actually flatting out a very short length of the helix, and bringing the top rake of the cutting edge to zero degrees. At one time in the past you used to be able to get drills with straight flutes for drilling brass.

You can have two bits of brass, and drill through one like a hot knife through butter, the other will grab the drill, screech like one thing, and cause all sorts of grief.

Ian S C

I suspect you're listening to the wrong people.

Most common brasses, like cast iron, are short chipping, producing a fine spray of swarf. Brass is usually machined with tools that have little, or no, rake. For instance a HSS toolbit for turning brass will be almost flat on the top surface. The issues with drilling brass are nothing to do with the chisel point or the drill point angle. They're all to do with the rake angle. The faster the helix the larger the rake angle. In a similar way to the turning tool the ideal drill for brass will have zero rake. In times gone by straight flute drills were available for brass. The idea of stoning the drill is to add a small 'flat' on the cutting edge, ie, zero rake. My personal experience is that it doesn't work that well: maybe I didn't stone the edges correctly? However, what does work is slow helix drills. For opening up larger holes I've also used slot drills, which tend to be slower helix than jobbers drills and hence don't 'grab'.

Brass and cast iron are always machined dry, whatever the operation. Using cutting fluid just results in a messy paste and actually stops the swarf from being cleared. I've never broken a tap in brass, including hundreds of holes tapped 8BA under power at 800rpm. The home made square thread taps I've shown in other posts easily cut a thread in brass dry. The final bronze nuts were another story!

There are presistent rumours that 'import' HSS isn't as good as the old stuff. I'd be interested to know what evidence you have regarding grain size in old versus new. What is the rough grain size in HSS? What sort of Ra values do you get turning brass and how do these correlate with the source of the HSS?

Andrew

Edit: It's good that Ian SC has confirmed the existence of straight flute drills. My statement was based on seeing them in my father's tool boxes 'ahem' years ago.

Edited By Andrew Johnston on 03/05/2016 12:32:17

I stone the cutting edge for drilling brass, just a couple of strokes. As said this gives a zero rake, even tho' just a small one. Usually a big improvement. I did try to have a set just for brass but over the years ,and lack of cash, They got mixed and I never noticed the difference. I would say that the stoned drills cut better in steel, seem to give a more accurate diameter hole.

Conversely, I have a set of very fast helix drills for aluminium and light alloy. Tools for the job.

Simply sharpening a std drill and diving into a bit of brass would require strong rubber pants, particularly when you are actually opening up an existing bore and there isn't a central chisel point to moderate progress. Apart from the rubber pants, you need to stand back and keep fingers and faces well clear, especially if using a pillar drill and a vise that is not firmly bolted down. More a question of HSE than HSS?

Years ago when drilling brass I had the mother of all snatches that scared me stiff. I made up a box of drills and with a diamond file took all the rake of the cutting edges. No trouble since.

I don't know why the drill edge mod for brass seems to work for some but not others but it's been discussed here on a number of occasions. I can only assume there are differences in the way we achieve it.

For my part - and very possibly out of ignorance - I never saw the need for the finesse of stoning or diamond lapping the drill. I just used a couple of quick touches on a grinding wheel (sometimes a third to even the two edges out). At most 10 seconds for the whole shebang.

Because of this, possibly I get a rather wider land and that's the difference. I don't know. Probably not the thing to do if you're going to regrind the drill to normal after use (some people do apparently).

This is the 1/2" drill from the modified set that I keep for brass (actually partial set still because I do them as needed). Absolutely no tendency to pull in when opening a pre-drill ..... and the drill chuck stays on the Jacob's taper

Edited By Bandersnatch on 03/05/2016 22:48:38

I suspect that was my problem. But since it is just as cheap to buy a slow helix drill as a standard jobbers drill to modify I'm going to stick with the slow helix drills.

Andrew

Forgive me if I am stating the obvious, but:

The effect of this edge modification, or indeed the use of slow helix drills simply to reduce the 'top rake' of the cutting edge.

• In the lathe, we typically use zero rake for brass-turning tools, and
• On a clockmaker's 5-sided broach, the rake is negative

Both of these work exceptionally well ... so 'go compare'

MichaelG.

Edited By Michael Gilligan on 04/05/2016 09:42:55

Ah well, what is obvious is that I need to work on the clarity of my written English...........

Andrew

Sorry, Andrew ... I jumped into this thread rather late, and hadn't noticed that you had already made the same comparison.

The blushes are for me

MichaelG.

I have followed this thread with curiosity. I have drilled brass for years without any problems. Take a new drill and remove the rake with a stone, use only a couple of strokes of the stone just enough to give a visible face when viewed with a magnifying glass. Drill the hole dry but if I get fed up with the screaming I wet the drill with white spirit - this does nothing, not even reduce the noise (old habits die hard). After using the drill put it aside for future use.

I don't know how fast you can machine brass but it is probably much faster than you think or even recommended. Brass has become a material of choice for rapid prototyping so I guess it can be machined at very high speeds.

JA

To [maybe] justify my inclusion in the discussion ... I would emphasise that I mentioned the 5-sided broach because it informs our understanding of what [in the present context] constitutes a 'sharp edge'.

MichaelG.